ASTR Sample Final [Spring 2017]

100. Massive-star supernovae and white-dwarf supernovae work equally well as standard candles for measuring cosmic distances.

False

82. The observable universe is the same size today as it was a few billion years ago.

False

83. A terrestrial world's lithosphere is a thin layer of rock that lies between the mantle and crust.

False

86. Dark energy is the energy contained in dark matter.

False

88. The inner core of the Earth is made of liquid iron and nickel

False

90. A star more luminous than our Sun will have a habitable zone that is narrower and farther from the star than the habitable zone of the Sun

False

91. Sandstone is a common type of metamorphic rock

False

94. All the planets in the solar system have at least one moon.

False

96. Nuclear fusion is the process by which large nuclei break up into smaller nuclei with the release of energy.

False

98. If they existed, and if they were watching, a civilization at the center of the Milky Way could have detected our first TV signals by now.

False

99. In the cosmic timeline for the universe starting at the Big Bang, we live in the Planck era.

False

81. The frost line is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense.

True

84. A protostar is a star that is still in the process of forming.

True

85. Robert Goddard started launching liquid-filled rockets in the United States in 1926.

True

87. A photoautotroph gets its energy from the Sun and its carbon from the its environment

True

89. The process by which molecules escape from a solid directly into the gas phase is called sublimation

True

92. Water is present on the Moon in the form of ice in polar craters

True

93. The most important source of Earth's early atmosphere was outgassing by volcanoes on the Earth's surface.

True

95. The ratio of an animal's brain weight to body weight is thought to be roughly proportional to its intelligence.

True

97. We have already launched spacecraft whose orbits will carry them into interstellar space

True

64. Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true? a. A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage. b. All the stars in the cluster will become main-sequence stars at about the same time. c. All the stars in the cluster will have approximately the same luminosity and surface temperature. d. All the stars in the cluster will be of about the same mass.

a. A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.

3. The first living organisms probably were: a. Cells without nuclei that used RNA as their genetic material. b. Cells with nuclei that used RNA as their genetic material. c. Cells without nuclei that used DNA as their genetic material. d. Cells with nuclei that used DNA as their genetic material.

a. Cells without nuclei that used RNA as their genetic material.

30. Why do we call dark matter "dark"? a. It emits no radiation that we have been able to detect. b. It blocks out the light of stars in a galaxy. c. It contains large amounts of dark-colored dust. d. It is dark brown or dark red in color.

a. It emits no radiation that we have been able to detect.

9. Which of the following best describes how the Drake equation is useful? a. It helps us understand what we need to know in order to determine the likelihood of finding other civilizations. b. It has allowed us to determine the number of civilizations in the Milky Way Galaxy. c. It allows us to calculate the masses of planets orbiting other stars. d. It tells us what wavelengths of light will be most useful to examine in the search for extraterrestrial intelligence.

a. It helps us understand what we need to know in order to determine the likelihood of finding other civilizations.

78. What is the role of the magnetosphere in Earth's habitability? a. It shields the atmosphere from particles of the solar wind. b. It shields Earth from many asteroid and comet impacts that would otherwise occur. c. It produces the lights of the aurora. d. It blocks the loss of atmospheric gas to thermal escape.

a. It shields the atmosphere from particles of the solar wind.

76. What are stromatolites? a. Living colonies of bacteria b. Fossils of large, mat-shaped plants that still live in western Australia c. Microscopic fossil structures that look like individual bacteria d. Rocks thought to be fossils made by ancient microbes

a. Living colonies of bacteria

79. To measure a rock's age, we must a. Measure the ratios of different isotopes within it b. Identify its mineral structure c. Determine its chemical composition d. Determine the type of rock it is

a. Measure the ratios of different isotopes within it

8. From hottest to coolest, the order of the spectral types of stars is _________. a. OBAFGKM b. ABFGKMO c. OMKGFBA d. OBAGFKM

a. OBAFGKM

20. The first successful launch of a satellite into Earth orbit was accomplished by ________. a. The Soviet Union in 1957 b. Russian scientist Konstantin Tsiolkovsky in 1894 c. American scientist Robert Goddard in 1926 d. The United States in 1955

a. The Soviet Union in 1957

16. Which ingredient are you most likely to find if you randomly choose a small moon of one of the jovian planets to examine? a. Water ice. b. Organic molecules. c. Liquid water. d. An abundance of heavy metals, such as gold.

a. Water ice.

62. Which of the following statements best describes the current state of understanding regarding the apparent acceleration of the expansion of the universe? a. We have moderately strong evidence that the acceleration is real, but essentially no idea what is causing it. b. The acceleration is very important in the cosmos today, but the evidence indicates that it will eventually slow down, allowing the universe to recollapse. c. The acceleration probably is not real, and what we attribute to acceleration is probably just a misinterpretation of the data. d. The cause of the acceleration is well-understood, and attributed to the particles that make up dark energy.

a. We have moderately strong evidence that the acceleration is real, but essentially no idea what is causing it.

21. What do we mean when we say that the terrestrial worlds underwent differentiation? a. When their interiors were molten, denser materials sank toward their centers and lighter materials rose toward their surfaces. b. Their surfaces show a variety of different geological features resulting from different geological processes. c. The five terrestrial worlds all started similarly but ended up looking quite different. d. They lost interior heat to outer space.

a. When their interiors were molten, denser materials sank toward their centers and lighter materials rose toward their surfaces.

72. Global warming refers to ________. a. an increase in Earth's average surface temperature b. the idea that every place on Earth is getting warmer c. the warming that will occur on Earth as the Sun brightens in the future d. any warming caused by human activity

a. an increase in Earth's average surface temperature

68. When we say that liquid water is unstable on Mars today, we mean that ________. a. any liquid water on the surface would quickly freeze or evaporate b. a cup of water would shake uncontrollably c. it is impossible for liquid water to exist on the surface even for a very short time d. any liquid water on the surface would quickly undergo chemical reactions converting the water molecules to other molecules

a. any liquid water on the surface would quickly freeze or evaporate

37. The fact that many different organisms on Earth have developed eyesight provides evidence for a. convergent evolution b. cross-breeding c. artificial selection d. genetic mutations

a. convergent evolution

43. The planet Venus is often referred to as the Earth's "sister planet" because a. it is almost the same size and density b. it looks like the Earth through a telescope c. its atmosphere has the same composition d. its surface is very similar

a. it is almost the same size and density

66. Which of the following sequences correctly describes the stages of life for a low-mass star? a. protostar, main-sequence, red giant, white dwarf b. protostar, red giant, main-sequence, white dwarf c. protostar, main-sequence, white dwarf, red giant d. red giant, protostar, main-sequence, white dwarf

a. protostar, main-sequence, red giant, white dwarf

47. Stars of spectral type A and F are considered ________. a. reasonably likely to have habitable planets, but much less likely to have planets with complex plant- or animal-like life b. unlikely to have habitable planets c. reasonably likely to have Earth-like planets with complex plant- and animal-like life d. unlikely to have planets of any kind

a. reasonably likely to have habitable planets, but much less likely to have planets with complex plant- or animal-like life

67. The color of a star is a measure of its a. surface temperature b. chemical composition c. mass d. size

a. surface temperature

32. Biologists have found that life on Earth can a. survive over a wide range of environmental conditions b. only survive on the surface of the Earth c. survive over only a very narrow range of environmental conditions d. survive only in the presence of sunlight

a. survive over a wide range of environmental conditions

53. Our solar system consists of ________. a. the Sun and all the objects that orbit it b. the Sun and several nearby stars, as well as the planets and other objects that orbit these stars c. the Sun and the planets, and nothing else d. a few hundred billion stars, bound together by gravity

a. the Sun and all the objects that orbit it

6. What is the distinguishing characteristic that those doing radio SETI experiments look for? a. A signal containing the value of pi and other mathematical constants b. A signal that extends over only a narrow range of frequencies. c. A signal that is an echo of an Earthly broadcast. d. A signal using the Morse code.

b. A signal that extends over only a narrow range of frequencies.

22. The processes responsible for virtually all surface geology are _________. a. Convection, conduction, and radiation. b. Cratering, volcanisms, tectonics, and erosion. c. Accretion, differentiation, and radioactive decay. d. Eruptions, lava flows, and outgassing.

b. Cratering, volcanisms, tectonics, and erosion.

42. Evolutionary adaptations are related to changes that occur through time in a. lipids b. DNA c. carbohydrates d. proteins

b. DNA

55. Why are fossils of early life on Earth more rare than fossils of plants and animals from the past few hundred million years? a. We find fossils in sedimentary layers, and no sediments were deposited until just a few hundred million years ago. b. Early organisms lacked skeletons and other hard structures that are most likely to be fossilized. c. Life was far less abundant prior to a few hundred million years ago. d. Fossils could not form before there was oxygen in the atmosphere.

b. Early organisms lacked skeletons and other hard structures that are most likely to be fossilized.

14. Earth has far less atmospheric carbon dioxide than Venus because: a. Earth was born with less of this gas. b. Earth's carbon dioxide is locked up in carbonate rocks. c. Earth's carbon dioxide was lost in the giant impact that formed the moon. d. Earth's carbon dioxide was lost into space because of its weaker magnetic field.

b. Earth's carbon dioxide is locked up in carbonate rocks.

74. According to the fossil evidence, modern humans (Homo Sapiens) a. Evolved from chimpanzees b. Evolved on a lineage that split from other apes 6 million years ago c. Evolved from Neanderthals d. Have remained unchanged for the past 2 million years

b. Evolved on a lineage that split from other apes 6 million years ago

52. According to the leading hypothesis, what happened to most of Mars's ancient atmospheric gas? a. It became bonded into surface rock. b. It was stripped away by the solar wind. c. It is trapped under the Martian surface d. It is now frozen in the polar caps.

b. It was stripped away by the solar wind.

15. Natural selection is a name given to: a. The occasional mutations that occur in DNA. b. The mechanism by which advantageous traits are preferentially passed on from parents to offspring. c. A theory that competes with the Theory of Evolution to explain the diversity of life on Earth. d. The idea that organisms can develop new characteristics during their lives and then pass these to their offspring.

b. The mechanism by which advantageous traits are preferentially passed on from parents to offspring.

12. We can recognize the oldest surface regions of Mars by the fact that they have a. The most evidence of water flows. b. The most impact craters. c. The most volcanoes. d. The smoothest surface.

b. The most impact craters.

56. In general, how does the size and location of a star's habitable zone depend on the star's mass? a. The smaller (less massive) the star, the larger and the closer-in the habitable zone. b. The smaller (less massive) the star, the smaller and the closer-in the habitable zone. c. The habitable zone is always about the same size, but its location moves inward for smaller stars. d. The smaller (less massive) the star, the larger and the farther-out the habitable zone.

b. The smaller (less massive) the star, the smaller and the closer-in the habitable zone.

69. A light-year is ________. a. a unit of speed b. a unit of distance c. an expression used for anything very large d. a unit of time

b. a unit of distance

46. The wavelengths of radiation from a star that is moving toward us a. can be longer or shorter depending on the distance to the star b. are shorter than if the star were not moving c. are longer than if the star were not moving d. are the same as if the star were not moving

b. are shorter than if the star were not moving

44. Why does the Doppler shift method of detecting extrasolar planets only give us the minimum mass of a planet? a. because we don't necessarily know the density of the planet b. because we don't necessarily know the angle the planet's orbit makes with our line of sight c. because we don't necessarily know the diameter (size) of the planet d. because we don't necessarily know the mass of the parent star very

b. because we don't necessarily know the angle the planet's orbit makes with our line of sight

48. The Hertzsprung-Russell (H-R) diagram is a way of ________. a. classifying planets according to their sizes and the distances at which they orbit their stars b. classifying stars according to their surface temperatures and luminosities c. classifying stars according to their masses and ages d. classifying planets according to their orbital periods and the distances at which they orbit their stars.

b. classifying stars according to their surface temperatures and luminosities

70. The age of stars in a cluster can be determined by a. fitting the position of the main sequence to the Sun. b. determining the main sequence turnoff point. c. finding pulsating variable stars in the cluster. d. finding spectroscopic binaries in the cluster.

b. determining the main sequence turnoff point.

25. The outward pressure of hot gas in the Sun a. is increasing the Sun's diameter. b. is balanced by the inward gravitational pressure. c. is cooling the photosphere. d. is responsible for variations in the sunspot cycle.

b. is balanced by the inward gravitational pressure.

36. If a scientific model generates a prediction that is not confirmed experimentally, a. the experimental data must be modified to be consistent with the model b. it must be initially revised and eventually abandoned if it continues to be inconsistent with experiments c. it must be assumed that there are errors in the experiment d. it must immediately be abandoned

b. it must be initially revised and eventually abandoned if it continues to be inconsistent with experiments

34. A sterilizing impact is one during which a. all life on a planet is destroyed b. most life on the surface of a planet is destroyed but life in the oceans or beneath the surface might survive c. a planet is fragmented into pieces d. life on a planet is rendered incapable of reproduction

b. most life on the surface of a planet is destroyed but life in the oceans or beneath the surface might survive

17. Based on DNA studies, it seems that all life on Earth _________. a. arose from one of five distinct ancestors that lived about two billion years ago b. shares a common ancestor c. requires oxygen to survive d. to one of just two kingdoms: plants and animals

b. shares a common ancestor

54. In an extrasolar planetary system containing a single planet, the parent star is measured to move about its center of mass every 24 years. Given this, what is the orbital period of the planet? a. 48 years b. 12 years c. 24 years d. this cannot be determined from this observation

c. 24 years

77. How do we determine where an organism belongs in the tree of life? a. By observing its physical characteristics b. By the age of its oldest known fossils c. By comparing its DNA to that of other organisms d. By classifying its metabolism according to its sources of nutrients and energy

c. By comparing its DNA to that of other organisms

31. How is/was the Kepler mission searching for extrasolar planets? a. By looking for small changes in a star's position b. By looking for events in which the star temporarily disappears from our view c. By looking for small changes in a star's brightness d. By looking for small changes in a star's Doppler shift

c. By looking for small changes in a star's brightness

19. What is a planetary nebula? a. The remains of a high-mass star that has exploded. b. Gas created from the remains of planets that once orbited a dead star. c. Gas ejected from a low-mass star in the final stage of its life. d. Interstellar gas from which planets are likely to form in the not-too-distant future.

c. Gas ejected from a low-mass star in the final stage of its life

23. Frozen lakes often have liquid water beneath their icy surfaces primarily because a. Earth's internal heat keeps the water liquid. b. Sunlight penetrates the ice and warms the water below. c. Ice floats and provides insulation to the water below. d. Volcanic vents are present in the deepest part of the lake.

c. Ice floats and provides insulation to the water below.

71. Io is covered in volcanoes while Europa is covered in ice because _______________. a. Io is larger than Europa b. Io receives much more sunlight than Europa c. Io is subject to stronger tidal heating than Europa d. Io is closer to Earth

c. Io is subject to stronger tidal heating than Europa

35. Pluto and Eris are members of the a. Asteroid Belt b. Jovian family of planets c. Kuiper Belt d. Oort Cloud

c. Kuiper Belt

57. Which of the following statements about matter-antimatter engines is not true? a. Matter-antimatter reactions represent the most efficient possible reactions in terms of energy release. b. One of the major challenges to developing matter-antimatter engines is finding a way to store antimatter after it is produced. c. Matter-antimatter engines would be great in theory, but to date we have no evidence that antimatter even exists. d. Spacecraft powered by matter-antimatter engines could probably reach speeds of more than half the speed of light.

c. Matter-antimatter engines would be great in theory, but to date we have no evidence that antimatter even exists.

60. What is the Fermi Paradox? a. Interstellar travel is possible yet would take an infinite amount of time because of relativistic time-dilation. b. We would be unable to detect an Earth-like planet even at a distance of a few light years. c. Reasonable assumptions predict that a galactic civilization should have already arisen in the Milky Way. Yet, we have absolutely no evidence for it. d. Galactic civilizations, like ours, seem forbidden by the laws of physics.

c. Reasonable assumptions predict that a galactic civilization should have already arisen in the Milky Way. Yet, we have absolutely no evidence for it.

28. Why is Europa considered a good candidate for the possible existence of life? a. It is located within our Sun's habitable zone. b. It has a thick atmosphere with a surface pressure greater than that on Earth. c. Strong evidence suggests that it has a deep, subsurface ocean of liquid water. d. The Galileo spacecraft found strange seasonal changes on its surface that look like they could be due to life.

c. Strong evidence suggests that it has a deep, subsurface ocean of liquid water.

80. Which of the following is not a key property of life? a. The maintenance of order in living cells b. The ability to evolve over time c. The ability to violate the second law of thermodynamics d. The ability to reproduce

c. The ability to violate the second law of thermodynamics

75. In regard to Percival Lowell's claims of a vast canal system on Mars, Alfred Russel Wallace wrote "[a network of canals,] as Mr. Lowell describes, would be the work of a body of madmen rather than of intelligent beings." Why? a. The canals all connected to the polar caps. b. Only a race of giants could have built such huge canals. c. The canals claimed by Lowell ran in straight lines for great distances. d. Though he saw lots of canals, Lowell did not see any cities.

c. The canals claimed by Lowell ran in straight lines for great distances.

4. Why don't we expect to find life on planets orbiting high-mass stars? a. The high-mass stars emit too much ultraviolet radiation. b. The stars are too hot to allow for life. c. The lifetime of a high-mass star is too short. d. Planets cannot have stable orbits around high-mass stars.

c. The lifetime of a high-mass star is too short.

45. What is an animal's encephalization quotient (EQ)? a. The ratio of the cortex size to the size of the rest of the brain b. The time since the animal split off from its last common ancestor c. The ratio of its brain mass to body mass d. The result of an IQ test given to the animal

c. The ratio of its brain mass to body mass

5. Early life arose in an oxygen-free environment, but if any of these microbes had somehow come into contact with oxygen, the most likely effect would have been: a. Nothing at all b. An increase in their metabolic rates c. To kill the microbes. d. To initiate photosynthesis in these microbes.

c. To kill the microbes.

49. The larger of the jovian moons ________. a. have a diameter about 10% that of Jupiter b. are larger than Earth c. are larger than Mercury but smaller than Mars d. are smaller than any of the planets

c. are larger than Mercury but smaller than Mars

39. Planetary science predicts that planets around other stars should be a. Earth-like b. nonexistent c. common d. relatively rare

c. common

1. The Sun's habitable zone _________. a. consists only of Earth, since Earth is the only planet known to be inhabited b. extends from the orbit of Earth to the orbit of Jupiter c. extends from some place a little beyond the orbit of Venus to some place near the orbit of Mars d. extends from just beyond the orbit of Mercury to just beyond Earth's orbit

c. extends from some place a little beyond the orbit of Venus to some place near the orbit of Mars

26. The most common element in the sun is a. helium b. iron c. hydrogen d. nitrogen

c. hydrogen

61. The Martian "blueberries" are ________. a. small, rocky spheres thought likely to contain fossilized ancient microbes b. layered boulders that look like the sediment layers found in Earth's Grand Canyon c. pebble-sized spheres containing the mineral hematite d. bluish features seen in orbital photos

c. pebble-sized spheres containing the mineral hematite

38. Kepler's Third Law of planetary motion states that a. the further a planet is from the Sun, the faster it moves in its orbit b. an imaginary line joining the Sun and planet sweeps out equal areas in equal times c. the further a planet is from the Sun, the slower it moves in its orbit d. the orbits of planets are ellipses

c. the further a planet is from the Sun, the slower it moves in its orbit

24. Generally speaking, an extremophile is an organism that a. Thrives in conditions that would be lethal to humans and other animals. b. Could potentially survive in space. c. Is extremely small compared to most life on Earth. d. All of the above.

d. All of the above.

27. Why do asteroids and comets differ in composition? a. Comets formed from the jovian nebula, while asteroids did not. b. Asteroids are much larger than comets. c. Asteroids and comets formed at different times. d. Asteroids formed inside the frost line, while comets formed outside.

d. Asteroids formed inside the frost line, while comets formed outside.

40. Only one of the statements below uses the term theory in its correct, scientific sense. a. I wrote a theory that is 152 pages long. b. I have a new theory about the cause of earthquakes, and I plan to start testing it soon. c. Gravity is only a theory, so there's no reason to think it really happens. d. Einstein's theory of relativity has been repeatedly tested and verified.

d. Einstein's theory of relativity has been repeatedly tested and verified.

50. What do we mean when we say that a moon is in synchronous rotation? a. It orbits in its planet's equatorial plane. b. It rotates in the same amount of time as its planet. c. It has no axis tilt. d. It always keeps the same face toward its planet.

d. It always keeps the same face toward its planet.

10. Which of the following was not a major advantage of Copernicus's Sun-centered model over the Ptolemaic model? a. It made significantly better predictions of planetary positions in our sky. b. It offered a more natural explanation for the apparent retrograde motion of planets in our sky. c. It allowed the calculation of the orbital periods and distances of the planets. d. It did not require epicycles to explain planetary motion.

d. It did not require epicycles to explain planetary motion.

73. How does the habitable zone around a star of spectral type M compare to that around a star of spectral type G? a. It is larger and farther from the star b. It is larger and wider c. It is hotter and much brighter d. It is smaller and closer to the star

d. It is smaller and closer to the star

11. Which statement about Io is true? a. It is thought to have a deep, subsurface ocean of liquid water. b. It is the only moon in the solar system with a thick atmosphere. c. It is the largest moon in the solar system. d. It is the most volcanically active body in our solar system.

d. It is the most volcanically active body in our solar system.

18. Which of the following places is not generally considered a potential home for life in our solar system? a. Mars b. Titan c. Europa d. Jupiter's atmosphere

d. Jupiter's atmosphere

51. We have observed lakes of liquid methane or ethane on Titan, but we have not observed any lakes of liquid water. Is it possible that liquid water lakes also exist? Why or why not? a. Yes, but they exist only during Titan's summer season. b. Yes, but they are too small for our cameras to have detected so far. c. No, because like Mars, the atmospheric pressure is too low for water to be stable. d. No, because it is too cold.

d. No, because it is too cold.

65. Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system? a. It is impossible to say. b. They both occur in about equal numbers. c. Supernovae are more common. d. Planetary nebula formation is more common.

d. Planetary nebula formation is more common

13. What is considered to be the most likely explanation for the close-in orbits of "hot jupiter" extrasolar planets? a. They formed closer to their stars than Jupiter did. b. They show that the Nebular Theory needs to be modified. c. They are actually giant planets made of metal and rock. d. They formed far from their stars, like Jupiter, but then migrated inward.

d. They formed far from their stars, like Jupiter, but then migrated inward.

7. The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did these elements come from? a. They have been present in the universe since its birth. b. They were produced by gravity in the solar nebula as it collapsed. c. They were made by chemical reactions in interstellar gas. d. They were produced by stars that lived and died before our solar system was born.

d. They were produced by stars that lived and died before our solar system was born.

2. Astronomers infer that the universe is expanding because distant galaxies all appear to _________. a. be growing in size b. be made mostly of dark matter c. rotate rapidly d. be moving away from us, with more distant ones moving faster

d. be moving away from us, with more distant ones moving faster

58. At present, what is the primary way that astronomers carry out SETI programs (that is, search for extraterrestrial intelligence)? a. by analyzing the spectra of extra-solar planets in an attempt to detect oxygen b. by analyzing high-resolution images of nearby stars in search artificial structures c. by using X-ray telescopes to search for signals from extraterrestrial civilizations d. by using radio telescopes to search for signals from extraterrestrial civilizations

d. by using radio telescopes to search for signals from extraterrestrial civilizations

29. At the center of the Sun, nuclear fusion converts hydrogen into a. molecular hydrogen. b. radiation and elements such as carbon and nitrogen. c. radioactive elements such as uranium and plutonium. d. helium, gamma rays, and neutrinos.

d. helium, gamma rays, and neutrinos.

59. The Voyager I and II spacecraft visited the Jovian planets in the 1980s. When will they reach the distances of the nearest stars? a. in our children's lifetime b. in our grandchildren's lifetime c. thousands of years from now d. hundreds of thousands of years from now

d. hundreds of thousands of years from now

41. What do we mean by the half-life of a radioactive isotope? a. it is the amount of time a person can be exposed to radiation without getting sick b. it is the time for half the number of radioactive nuclei to become stable nuclei c. it is the amount of time for half of the nuclei to become radioactive d. it is the time for half the number of radioactive nuclei to decay

d. it is the time for half the number of radioactive nuclei to decay

33. The most numerous life on Earth is a. insects b. plants c. human beings d. microbes

d. microbes

63. Which two processes can generate energy to help a star maintain its internal thermal pressure? a. nuclear fusion and supernova b. nuclear fission and supernova c. nuclear fusion and nuclear fission d. nuclear fusion and gravitational contraction

d. nuclear fusion and gravitational contraction